The present invention relates to the field of optical reflectors and particularly to light assemblies which produce efficient and uniform illumination.
Light sources and reflectors have been the subject of design for many years. Many attempts have been made to design reflectors and light assemblies which provide efficient illumination. The need for improved light assemblies is particularly keen in the surgical and dental fields where high quality illumination is essential.
In the surgical and dental fields, illumination from the light assembly is frequently into a cavity. When illuminating a cavity, it is desirable that the cavity walls parallel to the optical axis of the light assembly receive adequate illumination. Also, it is desirable that a uniform flux distribution be available over the illuminated area so that variations in illumination do not interfere with observations. Also, shadowless illumination is desired. When a light path is interrupted, for example, by a medical instrument, the shadow effect should be minimized.
While the needs in the medical fields are important, light assemblies having specialized qualities of illumination are also important in other fields. For example displays of all types require specialized lighting. Art gallery displays frequently require uniform illumination and require illuminated areas of selected sizes.
Specialized light assemblies and reflectors are also required in projection systems which require a light source of uniform flux distribution in order to uniformly illuminate film or other objects.
Light assemblies and reflectors of many designs have long been known in which a light source is utilized with an elliptical or parabolic reflector. In U.S. Pat. No. 1,133,955, a light source placed at the focus of a parabolic reflector is described for reflecting light in lines parallel to the axis of the reflector. Light assemblies employing parabolic reflectors present a problem when they are illuminating a cavity. The portions of the cavity wall parallel to the optical axis of the parabolic reflector do not receive adequate illumination since the light rays are parallel to the wall. Also, parabolic reflectors do not minimize shadows. U.S. Pat. No. 1,133,955 also describes light originating from the first focus of an elliptical reflector being reflected to a point at the second focus of the reflector.
In order to illuminate any substantial area using an elliptical reflector, the illuminated plane conventionally has been moved away from the second focus of the ellipse, that is, to an out of focus location. For an out of focus illuminated plane the intensity of the incident light varies over the illuminated surface, that is, has a non-constant flux gradient. This condition results because the elliptical reflector projects a three-dimensional image of the light source at the second focus.
One solution to the problem of flux gradient was described in U.S. Pat. No. 1,253,813 where multi-faceted reflectors were described. The reflecting power of facets was reduced for the facets located in the tier located closer to the central axis of the reflector. While such reduction in reflective power makes the incident flux more uniform, the reduction in the reflectivity of the facets reduces the efficiency of the reflector. A reduction in the efficiency of the reflector, however, is exactly the antithesis of what is desired. Also, that patent had no correlation between the facet size and the illumated area.
In view of the above background, it is an objective of the present invention to provide an improved reflector which has greater efficiency because of a substantially uniform flux distribution over the illuminated area, and which reflects essentially all the incident flux emitted by the source into the illuminated area.